Solid-state imaging device, driving method thereof, and imaging system

ABSTRACT

A solid-state imaging device comprises a first pixel group includes a first photoelectric conversion unit that converts into electric charges reflection light pulses from an object irradiated with an irradiation light pulse, a first electric charge accumulation unit accumulating the electric charges in synchrony with turning on the irradiation light pulses, and a first reset unit resetting the electric charges; and a second pixel group includes a second photoelectric conversion unit that converts the reflection light into electric charges, a second electric charge accumulation unit that accumulates the electric charges synchronously with a switching the irradiation light pulses from on to off, and a second reset unit that releases a reset of the electric charges converted by the second photoelectric conversion unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device, a drivingmethod thereof, and an imaging system.

2. Description of the Related Art

The speed of light is 3×10⁸ m/s. Since this is known, a distance to anobject can be measured by emitting a light pulse towards the object froma light source, receiving reflected light that is reflected from theobject, and measuring the delay time of the light pulse. The TOF(Time-Of-Flight) method is a method for measuring the distance to anobject by measuring the flight time of the light pulse. A distancemeasurement range with respect to a delay time measurement range can beread and, for example, and if an apparatus were available for which thedelay time measurement range is 1 μs and the delay time measurementresolution is 1 ns, then a 150 m range could be measured with a 15 cmresolution, and the apparatus could be used as an on-board distancesensor for vehicles.

Technology has been proposed that acquires a two-dimensional image forranging by applying this principle to a solid-state imaging device.Japanese Patent Application Laid-Open No. 2004-294420 discussestechnology that uses a CMOS-type solid-state imaging device that has apixel configuration according to a charge sorting method.

A signal component corresponding to a precedent portion of a reflectionlight pulse that arrives after a delay when an irradiation light pulseis reflected from an object and a signal component corresponding to afollowing portion thereof are sorted by a switch. By detecting thesesignals for each pixel to determine a ratio between the precedentportion and the following portion, distance information can be obtainedfor each pixel.

Further, Japanese Patent Application Laid-Open No. 2004-045304 discussestechnology that uses the TOF method for a common CCD-type solid-stateimaging device.

According to a solid-state imaging device that employs TOF according toa charge sorting method, at least two memory components are required ina single pixel, and the sensitivity is prone to decrease because theaperture ratio of the photodiode cannot be increased. Thus, if the pixelsize is increased, it is difficult to provide a large number of pixels.Consequently, there is the problem that it is difficult to also use thedevice as a common multi-pixel solid-state imaging device.

Further, when applying the TOF method to a common CCD-type solid-stateimaging device, there is the problem that because delay components ofreflected light are detected in frame units, it is difficult to obtainan image for ranging at a high speed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a solid-state imagingdevice that can realize both general photography with a large number ofpixels and image for ranging photography, as well as a driving methodthereof and an imaging system.

A solid-state imaging device of the present invention comprises firstand second pixel groups each including a plurality of pixels, whereineach pixel of the first pixel group includes a first photoelectricconversion unit for converting, into an electric charge, a reflectionlight pulse from an object irradiated with an irradiation light pulse; afirst electric charge accumulation unit for accumulating the electriccharge converted by the first photoelectric conversion unitsynchronously with a timing of turning on the irradiation light pulse;and a first reset unit for reset of the electric charge converted by thefirst photoelectric conversion unit synchronously with a period ofturning off the irradiation light pulse, and each pixel of the secondpixel group includes a second photoelectric conversion unit forconverting, into an electric charge, the reflection light pulse from theobject irradiated with the irradiation light pulse; a second electriccharge accumulation unit for accumulating the electric charge convertedby the second photoelectric conversion unit synchronously with a timingof switching from on to off of the irradiation light pulse; and a secondreset unit for release a reset of the electric charge converted by thesecond photoelectric conversion unit synchronously with the timing ofswitching from on to off of the irradiation light pulse.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B include a sectional view of the pixel configuration of asolid-state imaging device, and a view that illustrates a channelpotential that shows a state after a reset according to a firstembodiment.

FIG. 2 is a view that illustrates a pixel circuit of a solid-stateimaging device according to the first embodiment.

FIGS. 3A and 3B include timing charts that illustrate a driving methodof the solid-state imaging device according to the first embodiment.

FIG. 4 is a timing chart that illustrates a driving method of asolid-state imaging device according to a second embodiment.

FIG. 5 is a circuit block diagram of an imaging system according to afourth embodiment.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

A solid-state imaging device according to a first embodiment of thepresent invention irradiates a light pulse at an object, and receives areflection light pulse that is reflected from the object with aplurality of pixel groups. The solid-state imaging device detects aprecedent component of a reflection light pulse with a first pixel groupsynchronously with a timing of turning on the irradiation light pulse,and detects a following component of the reflection light pulse with asecond pixel group synchronously with a period of turning off theirradiation light pulse. Detection of this distance information isperformed within one frame period.

The first embodiment of the present invention is described below usingFIGS. 1, 2 and 3. FIG. 1A is a sectional view of a pixel configurationaccording to the present embodiment. A conductivity type of asemiconductor is not limited to a type illustrated here, and a p-typeand an n-type may be the opposite of that illustrated here. A pixel sizeaccording to the present embodiment is 5 μm×5 μm. The pixels arearranged in a 3000×4000 arrangement to form a solid-state imaging devicewith 12,000,000 pixels.

A p-type impurity region (deep p-well) 311 is provided on a p-typesemiconductor substrate or a semiconductor substrate. A p-type impurityregion (p-well) 310 is provided in the p-type semiconductor substrate311. The p-type impurity region 310 and the p-type semiconductorsubstrate 311 are designed with different impurity concentrations. Forexample, the p-type impurity region 311 is designed with an impurityconcentration that is lower than that of the p-type impurity region 310.An n-type impurity region 301 is provided as a first semiconductorregion. The n-type impurity region 301 forms a p-n junction with thep-type impurity region 311 to function as a photoelectric conversionelement (photodiode: PD). An optical waveguide 302 is used to convergelight onto the photoelectric conversion element (photodiode: PD). Amicrolens 303 is used for guiding light to the optical waveguide.

A signal charge is transferred from the PD to a charge accumulatingportion (ST) 305 that serves as a charge accumulating region via a firsttransfer MOS transistor (MOS1) 1101 functioning as a transfer unit. Thetransfer MOS transistor 1101 is an MOS transistor that has an embeddedchannel structure. A control gate 306 formed by an MOS structure isprovided on the charge accumulating portion 305 in order to control thechannel potential thereof.

Further, the signal charge is transferred from the charge accumulatingportion (ST) 305 to a floating diffusion (FD) 308 via a second transferMOS transistor (MOS2) 307 that functions as a transfer unit. In thiscase, after undergoing charge/voltage conversion at the FD 308, theamplified signal is output as the pixel output. This process follows thesame principle as that of an ordinary CMOS sensor, and thus adescription thereof is omitted here. A light-shielding film 309 shieldslight from elements other than the photodiode.

An n-type impurity region 312 serves as a lateral overflow drain (OFD)for discharging excess charges. An OFD-MOS transistor 1102 forcontrolling the overflow drain is provided between the n-type impurityregion 312 and the PD. According to the present embodiment, the OFD-MOStransistor 1102 can be controlled for each row. A feature of the presentembodiment is that, in an image for ranging photography mode, the OFD312 and the OFD-MOS transistor 1102 for control thereof are associatedwith the driving timing of an irradiation light pulse source, and notwith discharge of excess charges. That is, as described later, a featureof the present embodiment is that, for a pixel group of odd-numberedrows (even-numbered rows), the OFD-MOS transistors 1102 are collectivelyactuated at the same timing as a timing of turning on/off a light pulse.At this time, a pixel structure having a global electronic shutterfunction is necessary for the group of odd-numbered row pixels and thegroup of even-numbered row pixels, respectively. According to thepresent embodiment, this is realized with the OFD 312 and the OFD-MOStransistor 1102 of each pixel, and a drive circuit (unshown) thatperforms collective light irradiation alternately with the group ofodd-numbered row pixels and the group of even-numbered row pixels.

FIG. 1B illustrates a channel potential that shows a state after areset. According to the construction of the present embodiment, even ifa voltage is applied that is enough to turn off the first transfer MOStransistor 1101, because the first transfer MOS transistor 1101 has anembedded channel structure, a place with a high channel potentialappears at a location that is at a certain depth from the surface.

FIG. 2 illustrates an equivalent circuit of this pixel. The upper halfin FIG. 2 illustrates a pixel of an odd-numbered row. The lower half inFIG. 2 illustrates a pixel of an even-numbered row. The circuit includesan overflow drain (OFD) 201, first transfer MOS transistors 207 and 212,and second transfer MOS transistors 209 and 214. The circuit furtherincludes charge accumulating portions (ST: electric charge accumulationunit) 208 and 213, photodiodes (PD: photoelectric conversion unit) 206and 211, a floating diffusion (FD) 215, an amplifier MOS transistor (SF)203, a selection MOS transistor (SEL) 204, and a reset MOS transistor(RES MOS) 202 that resets the floating diffusion portion. According tothe present embodiment, a single floating diffusion (FD) 215 andamplifier MOS transistor (SF) 203 are shared by two pixels in thevertical direction.

Next, a driving method of the solid-state imaging device of the presentembodiment is described using FIG. 3. FIG. 3A is a view that describesthe timing of a control signal of a pixel of an odd-numbered row. FIG.3B is a view that describes the timing of a control signal of a pixel ofan even-numbered row.

A light source (unshown) irradiates intermittent pulsed light at anobject in response to a light emission control signal φP that repeatedlyturns on and off alternately at a constant cycle. Timings P1, P2, P3, .. . Pn (unshown) are timings of irradiation light pulses. Theseirradiation light pulses are generated by controlling the light sourcewith an unshown light source control circuit. A time width t is a timewidth of a single irradiation light pulse. A control signal φTX1 is acontrol signal of the first transfer MOS transistor 207 in odd-numberedrow pixels. A control signal φTX2 is a control signal of the firsttransfer MOS transistor 212 in even-numbered row pixels. A controlsignal φOFD1 is a control signal of the OFD-MOS transistor (reset unit)205 in odd-numbered row pixels. A control signal φOFD2 is a controlsignal of the OFD-MOS transistor (reset unit) 210 in even-numbered rowpixels. As described later, these control signals are driven with anunshown drive circuit so as to be synchronized with the light emissioncontrol signal φP. According to the present embodiment, an infrared LEDlight source with a sufficiently fast response with respect to the lightemission control signal φP is utilized as a light source. To facilitatedescription, in the drawings the light emission control signal φP andthe light emission are depicted as completely matching. In practice,there is a delay in response to some extent. In this case, the problemis overcome by synchronizing the solid-state imaging device controlsignal with the light emission control signal φP beforehand by takinginto account the delay amount. Further, an unshown visible light cut-offfilter is provided at the front face of the solid-state imaging device.According to the present embodiment, the infrared LED light source isalso utilized for general multi-pixel photography.

A feature of the present embodiment is that a construction is adoptedthat uses odd-numbered row pixels and even-numbered row pixels toisolate and detect a reflection light pulse RP produced when anirradiation light pulse is reflected by an object and arrives at asolid-state imaging device after being delayed in accordance with thedistance from the object thereto. A component detected with odd-numberedrow pixels is taken as a precedent portion S1 and a component detectedwith even-numbered row pixels is taken as a following portion S2.Further, it is assumed that S1+S2=100%. When a distance to an object is0, S1=100% and S2=0%. As the distance increases, the proportion of S1decreases and the proportion of S2 increases. That is, the distance canbe calculated by measuring the proportions of S1 and S2. This is theprinciple of the TOF method. Since this ratio can be calculated for eachpixel, distance information that corresponds to each pixel of an imagecan be obtained.

First, operations in a case where the solid-state imaging deviceirradiates a single irradiation light pulse P1 and detects thereflection light pulse RP are described. In odd-numbered row pixels, insynchrony with a rising edge of the irradiation light pulse P1 theOFD-MOS transistor 205 is turned off and the transfer MOS transistor(MOS1) 207 is turned on. In synchrony with a falling edge of theirradiation light pulse P1, the OFD-MOS transistor 205 is turned on andthe transfer MOS transistor (MOS1) 207 is turned off. As a result, asignal charge corresponding to the precedent component S1 is generatedat a PD 206 by a reflection light pulse RP that arrives after a delaycorresponding to a distance to the object that is produced by reflectionof the irradiation light pulse P1. During this period, the signal chargeis simultaneously transferred to the charge accumulating portion (ST)208 (diagonal line portion of signal charge 1 in FIG. 3A). At this time,the OFD-MOS transistor 210 is turned on in the even-numbered row pixels,and at the PD 211 a signal charge of a precedent component of thereflection light pulse RP is discharged to an OFD 201. Although anexample in which the light emission timing and the light exposure timingare completely matching is illustrated in the drawings, the timings maydeviate as long as synchronization can be attained. At this time, thepotential is raised by applying a bias to the gate of the transfer MOStransistor (MOS1) 207, and a magnitude relation is created between thepotentials such that PD<MOS1<ST. By realizing this kind of potentialdistribution, even when driven in synchrony with light pulses emitted ina small period such as in the present embodiment, an electric chargegenerated at the PD 206 is quickly sent to the charge accumulatingportion (ST) 208 without being accumulated in the PD 206. It is assumedthat a condition at this time is that a complete transfer is realized.As a result, the detection accuracy of the component S1 of thereflection light pulse is improved. Further, photoelectric conversion ofthe reflection light pulse takes place at a different location and depthaccording to the incident angle and the like thereof. Since the lightquantity of a single light pulse is extremely small, according to thepresent embodiment a configuration is adopted such that at least thechannel potentials below the PDs 206 and 211 among paths on which agenerated electric charge can move become highest. Thus, according tothe present embodiment, even if electric charges are generated atlocations that are separated from the PDs 206 and 211, the chargesefficiently converge at the PDs 206 and 211 and are immediatelytransferred to the charge accumulating portions 208 and 213, to therebyraise the sensitivity. The overflow drain 201 has the following twofunctions. A first function is one that discards signal charges thatexceed a predetermined level to the substrate. The object of thisfunction is to prevent an excessive signal charge generated when lightof an excessive intensity is incident on a photosensitive portion in ageneral photography mode from affecting the surrounding photosensitiveportion. A second function is one that collectively resets a pixelregion. The object of this function is to act as a global electronicshutter. If a level at which the overflow drain 201 causes a signalcharge to overflow is intentionally lowered, a signal charge of thephotosensitive portion is discarded as an excessive charge even when thesignal charge is not excessive, and thus the sensitivity of thephotosensitive portion can be substantially lowered. Moreover, since theoverflow drain 201 is directly connected to the substrate, thecapacitance is small in proportion to the shape, and switching atseveral tens of MHz is also possible. Therefore, by setting a low levelwith respect to a level at which the overflow drain 201 causes a signalcharge to overflow in a phase at which it is not desired to detectlight, the sensitivity of the photosensitive portion can be modulated inconformity with the cycle of irradiation light.

In the even-numbered row pixels, an electric charge is transferred fromthe PD 211 to the charge accumulating portion (ST) 213 in a staggeredmanner with respect to the irradiation light pulse P1. That is, insynchrony with a falling edge of the irradiation light pulse P1, theOFD-MOS transistor 210 is turned off, a reset of the PD 211 is released,and the transfer MOS transistor (MOS1) 212 is turned on. After a time t,the OFD-MOS transistor 210 is turned on and the transfer MOS transistor(MOS1) 212 is turned off. As a result, a signal charge corresponding tothe following component S2 is generated during a period until thereflection light pulse RP arrives at the PD 211. During this period, thesignal charge is simultaneously transferred to the charge accumulatingportion (ST) 213 (diagonal line portion of signal charge 2 in FIG. 3B).At this time, the OFD-MOS transistor 205 is turned on in theodd-numbered row pixels, and in the PD 206 a signal charge of afollowing component of the reflection light pulse RP is discharged tothe OFD 201. When transfer is completed, the OFD-MOS transistor 210 isimmediately turned on and the PD 211 is reset.

Further, regarding the irradiation light pulses P2, P3, . . . Pn, byrepeating the same operation during one blanking period, signal chargescorresponding to the precedent components S1 for irradiation lightpulses of n times are accumulated in the charge accumulating portion 208of the odd-numbered row pixels. Similarly, signal charges correspondingto the following components S2 are accumulated in the chargeaccumulating portion 213 of the even-numbered row pixels. A measurabledistance is decided according to the length of a single light emittingperiod. Errors can be reduced by performing light pulse irradiationmultiple times within a single frame period, and determining thedistance based on the sum total of the light exposure quantities(accumulated electric charges) within the single frame period.

Thereafter, the selection MOS transistor (SEL) 204 is turned on.Subsequently, the second transfer MOS transistor (M0S2) 209 is turnedon, a signal charge of the charge accumulating portion (ST) 208 istransferred to the floating diffusion (FD) 215, and is read out to asignal line S via the amplifier MOS transistor (SF) 203. This operationis performed for the group of odd-numbered row pixels and the group ofeven-numbered row pixels that read out distance information, tosequentially read out the signals of all rows from the first row to thefinal row.

In general, it is not necessary for the resolution of an image forranging to be a resolution obtained by all pixels with respect to asubject. For example, when acquiring distance information to an extentwhere it is sufficient to know the front-to-rear relationship betweentwo subjects, it is enough for the resolution to be a fraction of thesubject resolution. According to the present embodiment, an image forranging is acquired with pixels that are thinned at a ratio of 1/3 inthe lengthwise direction and a ratio of 1/4 in a lateral direction. As aresult, an image for ranging can be read at high speed. However, sincethe delay time of reflected light is measured with two rows, if the tworows are separated, not only the image resolution, but also the distanceresolution decreases. Therefore, according to the present embodiment,adjacent rows are utilized as the two rows. That is, reading isperformed after thinning pixels in two-row units.

A case of performing general photography with 12,000,000 pixels(3000×4000) using the solid-state imaging device of the presentembodiment is described below. The OFD-MOS transistors 205 and 210 ofall pixels are turned on and electric charges of the PDs 206 and 211 aredischarged to the overflow drain (OFD) 201 to collectively reset allpixels. Next, the OFD-MOS transistors 205 and 210 are turned off, andsignal accumulation is performed for a desired accumulation time. Atthis time, signal charges generated at the PDs 206 and 211 aretransferred from the PDs 206 and 211 to the charge accumulating portions(ST) 208 and 213 via the first transfer MOS transistors (MOS1) 207 and212, and accumulated therein. The signal charges are transferred fromthe charge accumulating portions 208 and 213 to the floating diffusion(FD) 215 via the second MOS transistors 209 and 214, and afterundergoing charge/voltage conversion at the amplifier MOS transistor(SF) 203, the amplified signal is output as the pixel output. Thesolid-state imaging device of the present embodiment enables both imagefor ranging photography and this kind of general multi-pixelphotography.

Second Embodiment

A feature of a second embodiment of the present invention is that groupsof pixels of three rows are utilized when photographing an image forranging. A feature of this embodiment is that the precedent component ofa reflection light pulse is detected with a group of pixels in a firstrow, a following component of a reflection light pulse is detected witha group of pixels in a second row, and a visible light component isdetected when the reflection light pulse is turned off by a group ofpixels in a third row. FIG. 4 is a timing chart that illustrates adriving method of a solid-state imaging device according to the secondembodiment of the present invention that shows a driving pattern ofpixels in a third row. The driving patterns of pixels in the first rowand second row are the same as the driving patterns of pixels in theodd-numbered rows and even-numbered rows according to the firstembodiment. The pixel circuit is also the same as in the firstembodiment, and a description thereof is thus omitted here. Signals ofbackground light other than an irradiation light pulse are accumulatedin the group of pixels in the third row. Adjacent rows are utilized asthe first row, second row and third row. Since a solid-state imagingdevice having a resolution of 12,000,000 pixels (3000×4000) is utilizedfor the present embodiment also, it is not a problem to use the presentembodiment by dividing the pixels into three groups of rows whenphotographing an image for ranging. Further, an infrared LED lightsource is utilized as a light source, and a visible light cut-off filterfor cutting out background light is not used.

First, operations are described for a case where a single irradiationlight pulse P1 is irradiated and a reflection light pulse RP is detectedin a state in which there is a background light “Light”. Sinceoperations at pixels in the first row are the same as operations atpixels in odd-numbered rows in the first embodiment, and operations atpixels in the second row are the same as operations at pixels ineven-numbered rows in the first embodiment, a description thereof isomitted below. Driving to detect background light at pixels in the thirdrow is described below. A feature of this driving is that although it isnot necessary to drive pixels in the third row in synchrony with turningthe irradiation light pulse P1 on and off, in order to detect only thebackground light “Light” the accumulation operations are performed at atiming at which the reflection light pulse RP has not reached thesolid-state imaging device. In practice, a φTX1 period of pixels in thefirst row and a φTX2 period of pixels in the second row occurconsecutively, and this period with respect to the irradiation lightpulse Pn is taken as Tn. A control signal φTX3 is a control signal ofthe first transfer MOS transistors 207 and 212 of pixels in the thirdrow. A control signal φOFD3 is a control signal of the OFD-MOStransistors 205 and 210 in the third row. An accumulation operation ofpixels in the third row is performed during a period between Tn andTn+1. That is, the OFD-MOS transistors 205 and 210 of pixels in thethird row are turned off during this period, and the transfer MOStransistors (MOS1) 207 and 212 are turned on. The pulse width of φTX3 isset to be the same as the pulse width of φTX1 and φTX2. As a result, asignal charge (diagonal line portion of signal charge 3 in FIG. 4)corresponding to the background light “Light” is generated. In thisperiod, this signal charge is simultaneously transferred to the chargeaccumulating portions (ST) 208 and 213. At this time, in the pixels inthe first and second rows the OFD-MOS transistors 205 and 210 are turnedon, and signal charges generated by the background light “Light” at thePDs 206 and 211 are discharged to the OFD 201.

In the present embodiment, a precedent component of irradiation lightpulses P1 to Pn detected in the first row is denoted by S1, a followingcomponent of irradiation light pulses P1 to Pn detected in the secondrow is denoted by S2, and a background light component detected in thethird row is denoted by S3. Since the background light component S3 isincluded in S1 and S2, when the true precedent component is taken as S1′and the following component is taken as S2′, these components can bedetermined by the following expressions.

S1′=S1−S3

S2′=S2−S3

In contrast, when performing general photography, photography usingvisible light such as natural light can be performed by general drivingof a solid-state imaging device. Thus, it is not necessary to use avisible light cut-off filter or the like in order to eliminatebackground light. An ordinary camera can be applied for generalphotography.

Third Embodiment

A feature of a third embodiment of the present invention is that pixelsof a plurality of rows that are consecutive are added to acquire animage for ranging. A circuit in which two pixels in the verticaldirection share a single floating diffusion (FD) 215 and amplifier MOStransistor (SF) 203 similarly to the circuit shown in FIG. 2 accordingto the first embodiment is used as a circuit of a solid-state imagingdevice according to the present embodiment. In general, it is notnecessary for the resolution of an image for ranging to be a resolutionobtained by all pixels with respect to a subject. For example, whenacquiring distance information to an extent where it is sufficient toknow the front-to-rear relationship between two subjects, it is enoughfor the resolution to be a fraction of the subject resolution. Accordingto the present embodiment, an image for ranging is acquired byperforming pixel addition with respect to two pixels in the verticaldirection and two pixels in the horizontal direction. Addition for thevertical direction is performed at the floating diffusion (FD) 215, andaddition for the horizontal direction is performed within a memory(unshown) of a horizontal read circuit. A common method is used as theaddition method. However, since the delay time of a reflection lightpulse is measured with two pixel groups, adjacent blocks are utilizedfor the two row blocks for which addition is performed. Each of thefirst and second pixel groups include a plurality of pixel blocks asobjects to be subjected to pixel addition.

It is thereby possible to raise the sensitivity. Further, an image forranging can be read at an even faster speed. According to the presentembodiment, although addition of two pixels in the vertical direction isperformed, the form of pixel addition is not limited thereto.

Fourth Embodiment

FIG. 5 is a block diagram that illustrates a configuration example of animaging system (visible light photography camera) according to a fourthembodiment of the present invention. The present embodiment is anexample in which a solid-state imaging device 54 according to the secondembodiment is applied to a camera that photographs using visible lightfor. A shutter 51 is provided in front of a photographic lens (opticalsystem) 52 to control exposure. For general photography, it is alsopossible to control the accumulation time of electric charges by meansof an electronic shutter, without providing the mechanical shutter. Alight quantity is controlled as necessary by a diaphragm 53, and thephotographic lens 52 forms an image of light on the solid-state imagingdevice 54. A signal output from the solid-state imaging device 54 isprocessed at the imaging signal processing circuit 55, and is convertedfrom an analog signal into a digital signal by an A/D converter 56. Thedigital signal that is output is further subjected to arithmeticoperation processing at a signal processing unit 57. The processeddigital signal is stored in a memory unit 60, and sent to an externaldevice via an external I/F (interface) unit 63. The solid-state imagingdevice 54, the imaging signal processing circuit 55, the A/D converter56, and the signal processing unit 57 are controlled by a timinggenerator 58. The overall system is controlled by a whole controllingand arithmetic operation unit 59. When photographing an image forranging, the whole controlling and arithmetic operation unit 59 controlsa light pulse source (light pulse irradiation unit). For example, thelight pulse source is provided inside the whole controlling andarithmetic operation unit 59 and irradiates the irradiation light pulsesP1 to Pn. Control of the solid-state imaging device 54 whenphotographing an image for ranging is the same as that describedaccording to the second embodiment. Timing of the control of the OFD 201of a pixel and transfer of electric charges from the photodiodes 206 and211 to the charge accumulating portions 208 and 213 is performed by thetiming generator 58. In order to record an image on a recording medium62, an output digital signal passes through an I/F unit controllingrecording medium 61 that is controlled by the whole controlling andarithmetic operation unit 59 and recorded on the recording medium 62. Acommon photographic image and an image for ranging corresponding theretocan be recorded on the recording medium 62.

As described above, the signal processing unit 57 calculates a distanceto an object based on electric charges accumulated in the first electriccharge accumulation unit 208 and electric charges accumulated in thesecond electric charge accumulation unit 213.

The imaging system of the present embodiment can incorporate an imagefor ranging photography function into a general photography camera,which has been difficult to do conventionally, by using the solid-stateimaging device 54 according to the first to third embodiments.

According to the first to fourth embodiments, it is possible to detect adelay time of the phase of reflected light from an object with respectto an irradiation light for each pixel of a solid-state imaging device,and thereby acquire information regarding the distance to the object.Both general multi-pixel photography and photography of an image forranging can be realized using a single solid-state imaging device, andan image for ranging can be acquired at a high speed.

The first to third solid-state imaging devices have a first pixel group(for example, a group of pixels in odd-numbered rows) and a second pixelgroup (for example, a group of pixels in even-numbered rows) that eachinclude a plurality of pixels.

Each pixel of the first pixel group has a first photoelectric conversionunit (photodiode) 206, a first electric charge accumulation unit (chargeaccumulating portion) 208, and a first reset unit (OFD-MOS transistor)205. The first photoelectric conversion unit 206 converts reflectionlight pulses RP reflected from an object by irradiating irradiationlight pulses P1 to Pn at the object into electric charges. The firstelectric charge accumulation unit 208 accumulates electric chargesconverted by the first photoelectric conversion unit 206 in synchronywith a timing of turning on the irradiation light pulses P1 to Pn. Thefirst reset unit 205 resets the electric charge converted by the firstphotoelectric conversion unit 206 in synchrony with a period of turningoff the irradiation light pulses P1 to Pn.

Each pixel of the second pixel group has a second photoelectricconversion unit (photodiode) 211, a second electric charge accumulationunit (charge accumulating portion) 213, and a second reset unit (OFD-MOStransistor) 210. The second photoelectric conversion unit 211 converts areflection light pulse RP that is reflected from an object into anelectric charge. The second electric charge accumulation unit 213accumulates the electric charges converted by the second photoelectricconversion unit 211 in synchrony with a timing of switching theirradiation light pulses P1 to Pn from on to off. The second reset unit210 releases a reset of an electric charge converted by the secondphotoelectric conversion unit 211 in synchrony with a timing ofswitching the irradiation light pulses P1 to Pn from on to off.

At a plurality of pixels inside the first pixel group, exposure times ofthe first photoelectric conversion units 206 are collectively controlledaccording to electric charges accumulated in the first electric chargeaccumulation unit 208. Further, in a plurality of pixels inside thesecond pixel group, exposure times of the second photoelectricconversion units 211 are collectively controlled according to electriccharges accumulated in the second electric charge accumulation unit 213.

For example, the first pixel group is a group of pixels in a first rowand the second pixel group is a group of pixels in a second row.

According to the third embodiment, each of the first and second pixelgroups include a plurality of pixel blocks that are objects to besubjected to pixel addition.

According to the first to third embodiments, each pixel of the firstpixel group has a first transfer unit (transfer MOS transistor) 207 thattransfers an electric charge converted by the first photoelectricconversion unit 206 to the first electric charge accumulation unit 208.The first reset unit 205 is a first discharge unit that discharges theelectric charge converted by the first photoelectric conversion unit206, independently from the first electric charge accumulation unit 208.Further, each pixel of the second pixel group has a second transfer unit(transfer MOS transistor) 212 that transfers an electric chargeconverted by the second photoelectric conversion unit 211 to the secondelectric charge accumulation unit 213. The second reset unit 210 is asecond discharge unit that discharges the electric charge converted bythe second photoelectric conversion unit 211, independently from thesecond electric charge accumulation unit 213.

According to the second embodiment, a solid-state imaging device has athird pixel group that includes a plurality of pixels. Each pixel of thethird pixel group has third photoelectric conversion units 206 and 211,and third electric charge accumulation units 208 and 213. The thirdphotoelectric conversion units 206 and 211 convert a reflection lightpulse RP from an object into an electric charge. The third electriccharge accumulation units 208 and 213 accumulate the electric chargesconverted by the third photoelectric conversion units 206 and 211 duringa period of turning off the irradiation light pulses P1 to Pn.

The imaging system of the fourth embodiment includes the solid-stateimaging device 54 of the first to third embodiment, the light pulseirradiation unit (whole controlling and arithmetic operation unit) 59that irradiates the irradiation light pulses P1 to Pn, the opticalsystem (photographic lens) 52 that forms an image of light on thesolid-state imaging device 54, and the signal processing unit 57. Thesignal processing unit 57 calculates a distance to an object based onelectric charges accumulated in the first electric charge accumulationunit 208 and electric charges accumulated in the second electric chargeaccumulation unit 213.

According to the first to fourth embodiments, both general multi-pixelphotography and photography of an image for ranging for calculating adistance can be realized, and an image for ranging can be acquired at ahigh speed.

It is to be understood that each of the above described embodiments areintended to merely illustrate specific examples for implementing thepresent invention, and are not intended to limit the technical scope ofthe present invention. More specifically, the present invention can beimplemented in various forms without departing from the technicalconcept or the principal features thereof.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-060054, filed Mar. 12, 2009, which is hereby incorporated byreference herein in its entirety.

1. A solid-state imaging device comprising first and second pixel groupseach including a plurality of pixels, wherein each pixel of the firstpixel group includes a first photoelectric conversion unit forconverting, into an electric charge, a reflection light pulse from anobject irradiated with an irradiation light pulse; a first electriccharge accumulation unit for accumulating the electric charge convertedby the first photoelectric conversion unit synchronously with a timingof turning on the irradiation light pulse; and a first reset unit forreset of the electric charge converted by the first photoelectricconversion unit synchronously with a period of turning off theirradiation light pulse, and each pixel of the second pixel groupincludes a second photoelectric conversion unit for converting, into anelectric charge, the reflection light pulse from the object irradiatedwith the irradiation light pulse; a second electric charge accumulationunit for accumulating the electric charge converted by the secondphotoelectric conversion unit synchronously with a timing of switchingfrom on to off of the irradiation light pulse; and a second reset unitfor release a reset of the electric charge converted by the secondphotoelectric conversion unit synchronously with the timing of switchingfrom on to off of the irradiation light pulse.
 2. The solid-stateimaging device according to claim 1, wherein for the plurality of pixelsin the first pixel group, a period of irradiating the firstphotoelectric conversion unit with the irradiation light pulsecorresponding to the electric charge accumulated in the first electriccharge accumulation unit is collectively controlled, and for theplurality of pixels in the second pixel group, a period of irradiatingthe second photoelectric conversion unit with the irradiation lightpulse corresponding to the electric charge accumulated in the secondelectric charge accumulation unit is collectively controlled.
 3. Thesolid-state imaging device according to claim 1, wherein the first pixelgroup is a group of pixels in a first row, and the second pixel group isa group of pixels in a second row.
 4. The solid-state imaging deviceaccording to claim 1, wherein each of the first and second pixel groupscomprises a plurality of pixel blocks to be subjected to a pixeladdition.
 5. The solid-state imaging device according to claim 1,wherein each of the pixels included in the first pixel group includes afirst transfer unit for transferring the electric charge converted bythe first photoelectric conversion unit to the first electric chargeaccumulation unit, and the first reset unit is a first discharging unitfor discharging the electric charge converted by the first photoelectricconversion unit, independently from the first electric chargeaccumulation unit; and each of the pixels included in the second pixelgroup includes a second transfer unit for transferring the electriccharge converted by the second photoelectric conversion unit to thesecond electric charge accumulation unit, and the second reset unit is asecond discharging unit for discharging the electric charge converted bythe second photoelectric conversion unit, independently from the secondelectric charge accumulation unit.
 6. The solid-state imaging deviceaccording to claim 1, further comprising a third pixel group including aplurality of pixels, each including a third photoelectric conversionunit for converting, into an electric charge, the reflection light pulsefrom the object irradiated with the irradiation light pulse; a thirdelectric charge accumulation unit for accumulating the electric chargeconverted by the third photoelectric conversion unit within a periodduring which the irradiation light pulse is off.
 7. An imaging systemcomprising: a solid-state imaging device according to claim 1; a lightpulse irradiation unit for irradiating the object with the light pulse;an optical system for focusing an image of the light pulse onto thesolid-state imaging device; and a signal processing unit for calculatinga distance from the object based on the electric charge accumulate inthe first electric charge accumulation unit, and based on the electriccharge accumulate in the second electric charge accumulation unit.
 8. Adriving method of a solid-state imaging device comprising first andsecond pixel groups each including a plurality of pixels, wherein themethod comprising: in each pixel of the first pixel group, a firstphotoelectric conversion step for converting, into an electric charge, areflection light pulse from an object irradiated with an irradiationlight pulse; a first electric charge accumulation step for accumulatingthe electric charge converted in the first photoelectric conversion stepsynchronously with a timing of turning on the irradiation light pulse;and a first reset step for reset of the electric charge converted in thefirst photoelectric conversion step synchronously with a period ofturning off the irradiation light pulse, and, in each pixel of thesecond pixel group, a second photoelectric conversion step forconverting, into an electric charge, the reflection light pulse from theobject irradiated with the irradiation light pulse; a second electriccharge accumulation step for accumulating the electric charge convertedin the second photoelectric conversion step synchronously with a timingof switching from on to off of the irradiation light pulse; and a secondreset step for release a reset of the electric charge converted in thesecond photoelectric conversion step synchronously with the timing ofswitching from on to off of the irradiation light pulse.